This invention relates generally to monopulse radar systems and more particularly to angle error computation apparatus used therein for correcting received radar return signals in accordance with correction signals generated within the receivers in such radar systems.
As is known in the art, in a monopulse radar system the relative phase differences and gain imbalances between each receiver channel may have a significant effect on the angle tracking performance of the radar. The relative phase differences and gain imbalances are of two types: RF errors occurring prior to or in the monopulse comparator used to generate the sum and difference channels in the conventional monopulse receiver; and, gain imbalances and phase errors introduced in the RF and IF sections of the receiver after the sum and difference channels have been formed. Most of the latter errors can be negated by the use of pilot pulses as has been implemented in several systems in the field.
One such system, described in U.S. Pat. No. 3,794,998 issued to Pearson, Jr. et al, uses digital computation apparatus for generating from pilot pulses digital correction signals representative of pairs of quadrature components of video signals developed in the sum and each one of the difference channels. The quadrature components associated with the target return signals are then corrected digitally in accordance with the quadrature components associated with the digital correction signals. While such system has performed satisfactorily in removing the gain imbalances and phase errors introduced in the RF and IF sections of the receiver channels which are common to the target return signals and the pilot pulses, the system does not take into account the gain imbalances and phase errors introduced by the RF monopulse comparator in forming the sum channel and the difference channels. Once such gain imbalances and phase errors are introduced, they are not readily removed. Additionally, in high frequency monopulse radar systems in which signal wavelength is on the order of a few millimeters, the monopulse comparator must be quite small and conform to stringent phase and amplitude matching requirements. Thus, such a monopulse comparator is difficult to fabricate.